U.S. Pat. No. 3,624,164 discloses a continuous process for the preparation of alkali metal salts of nitrophenols by contacting a chloronitrobenzene with aqueous caustic at 180.degree.-250.degree. C. at autogenous pressure for 30 seconds to 10 minutes at a mole ratio of caustic to chloronitrobenzene of at least 2.0 and a power input into the feed streams of the reaction of at least 2.3 horsepower per 1,000 gallons of reaction volume. However, the aqueous solutions remaining after the removal of product therefrom contain a significant amount of product in the form of fines and soluble material that unless subjected to some recovery technique would be lost.
Other processes involving the preparation of a nitrophenol are disclosed in U.S. Pat. Nos. 3,283,011; 3,506,724; 3,804,907; 3,708,545 and 2,407,045.
U.S. Pat. No. 2,275,045 discloses a method for recovering phenolic compounds from aqueous solutions of the corresponding calcium phenolates by heating with water at elevated temperatures and under superatmospheric pressure to form calcium hydroxide and the free phenolic compound.
U.S. Pat. No. 2,743,301 discloses a method for separating the ortho- and para-isomers of alkali metal nitrophenates by adjusting the solution containing both to a low percentage of weight of both sodium hydroxide and sodium chloride and then maintaining the temperature at 35.degree.-55.degree. C. to precipitate the p-isomer.
The salting out of nitrophenols from aqueous solutions is disclosed in Journal of Applied Chemistry, USSR v. 50(9) 1977 by Korenman, Bortnikova and Nefedova.
The Effect of Salts in the Activity of p-Nitrophenol and its Anion in Aqueous Solution is the title of an article disclosed in the Russian Journal of Physical Chemistry, 45(4), 1971 by Sumskayn, Bugaevskii and Chernukha.